全文获取类型
收费全文 | 6117篇 |
免费 | 651篇 |
国内免费 | 486篇 |
专业分类
航空 | 3365篇 |
航天技术 | 1901篇 |
综合类 | 440篇 |
航天 | 1548篇 |
出版年
2023年 | 47篇 |
2022年 | 107篇 |
2021年 | 167篇 |
2020年 | 130篇 |
2019年 | 133篇 |
2018年 | 239篇 |
2017年 | 185篇 |
2016年 | 161篇 |
2015年 | 168篇 |
2014年 | 243篇 |
2013年 | 254篇 |
2012年 | 267篇 |
2011年 | 322篇 |
2010年 | 335篇 |
2009年 | 380篇 |
2008年 | 386篇 |
2007年 | 274篇 |
2006年 | 220篇 |
2005年 | 216篇 |
2004年 | 164篇 |
2003年 | 203篇 |
2002年 | 217篇 |
2001年 | 194篇 |
2000年 | 159篇 |
1999年 | 159篇 |
1998年 | 145篇 |
1997年 | 129篇 |
1996年 | 123篇 |
1995年 | 156篇 |
1994年 | 138篇 |
1993年 | 90篇 |
1992年 | 116篇 |
1991年 | 69篇 |
1990年 | 56篇 |
1989年 | 85篇 |
1988年 | 42篇 |
1987年 | 38篇 |
1986年 | 38篇 |
1985年 | 111篇 |
1984年 | 79篇 |
1983年 | 68篇 |
1982年 | 83篇 |
1981年 | 103篇 |
1980年 | 31篇 |
1979年 | 41篇 |
1978年 | 28篇 |
1977年 | 18篇 |
1974年 | 17篇 |
1973年 | 16篇 |
1972年 | 15篇 |
排序方式: 共有7254条查询结果,搜索用时 5 毫秒
781.
The paper discusses a method of designing the neural controller for two-channel control of a technical object by an example of the roll and yaw control depending on deviations, velocities and accelerations of their variation. 相似文献
782.
783.
J.K. Hargreaves 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2010
The paper summarises key facts and figures about the phenomenon of auroral radio absorption which are relevant to the problem of predicting its occurrence and intensity. The regions most affected are well known in terms of magnetic latitude (or L-value) and local time. The greater difficulty comes from its highly variable character. Exact predictions are never likely to be possible, but statistical forecasts, which would give the likelihood that some critical level will be reached or exceeded, may well be possible. At the present time it is suggested that they might be based on magnetic indices, since their prediction is already well established. Direct measurements of the solar wind, now available in real time, offer another possibility, perhaps to be considered in parallel. The substorm character of the absorption might also be applied, using the observed duration of absorption events and their known dynamics over the Earth’s surface, as an early warning. A comprehensive reference list is included. 相似文献
784.
目的介绍一种在Labwindows/CVI环境下调用Word的实现方法;方法结合具体的实例,实现对Word文档的调用;结果该方法可以按照规定的格式自动生成Word文档;结论提高了软件的效率和自动化程度。 相似文献
785.
The volume finite element in the form of hexahedron with nodal unknowns as components of the displacement vector and stress
tensor has been developed to analyze the shells of revolution. The displacement vector components for the inner point of the
finite element and the components of its stress tensor are expressed through the nodal unknowns using the method of vector
and tensor fields interpolation by the trilinear shape functions; that provides taking into account the finite element displacement
as a whole solid. The variational principle in a mixed formulation is applied to form the matrix of hexahedron deformation.
The efficiency of the proposed method for approximating the values being sought as vector and tensor fields in comparison
with the traditional method for approximating the values being sought as scalar fields is confirmed by a numerical example. 相似文献
786.
787.
G.L. Smith K.J. Priestley N.G. Loeb B.A. Wielicki T.P. Charlock P. Minnis D.R. Doelling D.A. Rutan 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
The Clouds and Earth Radiant Energy System (CERES) project’s objectives are to measure the reflected solar radiance (shortwave) and Earth-emitted (longwave) radiances and from these measurements to compute the shortwave and longwave radiation fluxes at the top of the atmosphere (TOA) and the surface and radiation divergence within the atmosphere. The fluxes at TOA are to be retrieved to an accuracy of 2%. Improved bidirectional reflectance distribution functions (BRDFs) have been developed to compute the fluxes at TOA from the measured radiances with errors reduced from ERBE by a factor of two or more. Instruments aboard the Terra and Aqua spacecraft provide sampling at four local times. In order to further reduce temporal sampling errors, data are used from the geostationary meteorological satellites to account for changes of scenes between observations by the CERES radiometers. 相似文献
788.
V. Anmireddy R. VasudevanD. Anand T.V. RaoB.V.N. Kapardhi D. TrivediR.K. Manchanda 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2010
Highly sophisticated balloon-borne scientific payloads have stringent requirement on the telemetry and command system. The development and fabrication of the on-board TT&C package for telemetry, tracking, command, safety and ranging for these experiments is done in-house at the National Balloon Facility (NBF) at Hyderabad. In the last few years, we have made major improvements both in the ground station and the on-board sub-systems, thereby improving the data quality, data handling speed and the general flight control along with aviation safety. The new system has telemetry data rate up to 1 Mbps. A reduction in weight, power and cost of the reengineered on-board integrated package has also lead to the ease of operation during field tests prior to launch and at remote recovery sites. In this paper, we describe the details of the new control package, its flight performance and our plans for portable S-band telemetry and telecommand system to cater to the balloon flights from Antarctic station and long duration balloon flights. 相似文献
789.
A. Yu. Liss 《Russian Aeronautics (Iz VUZ)》2012,55(2):136-143
We present the materials, which substantiate the application of a rather simple approximate method of accounting for disturbances of the airflow around the helicopter main rotor blades; in this case, the disturbances are caused by vortices that come down from the blade ends. It is shown that these disturbances influence significantly the varying blade loads. 相似文献
790.
We present the results of investigation of the dynamics of (99942) Apophis asteroid, which will undergo a very close encounter
with the Earth on April 13, 2029. The region of possible motions of the asteroid is considered on the time interval (2004,
2040). In addition, it is shown that an increase of the observational interval (2004, 2006) until 2008 allowed us to reduce
significantly the area of possible motions. All investigations were performed by numerical methods with the help of algorithms
and software developed by us in the environment of parallel programming using the SKIF Cyberia multiprocessor computer of
the Tomsk State University. 相似文献